Soft-bodies organisms rarely preserve as fossils in the geologic record. Low preservation potential results from the absence of hard-parts, predation, decay and reworking of sediment. This low preservation potential is particularly true for soft bodies organisms deposited in coarser grained substrates such as sandy beaches. Against great odds, the Late Cambrian (~510 Ma) Mt. Simon and Winewoc Formations of central Wisconsin preserve among the world's best known soft-bodied fossils. The Krukowski Quarry , located on County Highway C in Mosinee, contains among the best preserved jellyfish (scyphozoan medusae), Climactichnites and Protichnites fossils known on Earth! The medusae fossils are particularly outstanding as undisputed pre-Devonian examples are known from only two localities: St. Johns in New Brunswick Canada and Mosinee, Central Wisconsin (Hagadorn, Dott and Damrow, 2002)

Photograph within Krukowski Quarry Site, Mosinee, Wisconsin

Sunset at Krukowski Quarry, Mosinee wherein Cambrian quartz arenite of the Mt. Simon and Wonewoc Formation is exposed along bedding planes. Hundreds of medusae occur  with Climactichnites and Protichnites. The Mt. Simon and Wonewoc Formations were deposited along a sandy, equatorial beach. The Krukowski Quarry excavates quartz arenite rock deposited as fine to medium grained siliciclastic sand exposed on sandflats of an intertidal zone, possibly as part of a barrier island system (Dott, 1974).


Photo of a climactichnites fossil oriented transverse to ripple marks

            Photo of a climactichnites fossil oriented transverse to ripple marks


photograph of Medusae fossil, Mosinee, Wisconsin

Scyphozoan medusae ("jellyfish")

Go To: Medusae

Go To: Cambrian Arthropods

Go To: Climachtichnites


Dott, R. H., Jr., 1974, Cambrian Tropical Storm Waves in Wisconsin: Geology, v. 2, p. 243-246.

Hagadorn, J. W., Dott, R.H., Jr., and Damrow, D., 2002, Stranded on a Late Cambrian Shoreline: Medusae from Central Wisconsin: Geology, v. 30, p. 147-150.Online version at:

Yochelson, E.L.and Fedonkin, M.A., 1993, Paleobiology of Climactichnites, an enigmatic Late Cambrian fossil: Smithsonian Contributions to Paleobiology, no. 74, 74p.

Yochelson, E.L.and Fedonkin, M.A., 1991, Paleozoic Trail: National Geographic Research and Exploration, v. 7, no. 4, p. 453-455.

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